Molten carbonate fuel cells are well known in the art and are described, for example, in U.S. Pat. Nos. 4,009,321 and 4,079,171. The electrolyte in this type of cell is solid at room temperatures and is a molten liquid at operating temperatures which generally range between 500.degree. C. and 750.degree. C. Some well known electrolytes of this type are the alkali metal carbonate compositions such as ternary lithium-potassium-sodium carbonate compositions and binary lithium-potassium, lithium-sodium, or potassium-sodium carbonate compositions. The electrolyte is disposed within a substantially inert matrix sandwiched between an anode and a cathode electrode. In addition to having structural integrity, the matrix, in combination with the electrolyte, must provide complete separation of the fuel and oxidant gases disposed on opposite sides thereof. The electrolyte and matrix combination is often referred to as an electrolyte tile. The matrix is usually made from submicron ceramic particles which are compatible with the fuel cell environment. For example, lithium aluminate is substantially inert to the ternary and binary carbonate compositions mentioned above, and may be used as the matrix material in cells incorporating those types of electrolytes.
Typically, such tiles are produced by compression molding the inert material in admixture with the alkali metal carbonates. This method of producing the matrix structure suffers from many disadvantages. Compression molding is a relatively expensive forming method requiring relatively large amounts of time, energy and capital investment. The resultant molded tile is a relatively thick, fragile ceramic sheet. Accordingly, it is subject to cracking, and great care must be taken in the design of the fuel cell to provide a flat surface for such sheet to insure minimal flexural and compressive forces on the tile until heated above its melt point.
The poor handleability and critical tolerance requirements dictated by the use of this type of a matrix structure make scale-up to commercial sizes and quantities unattractive. In addition, a life-limiting, functional problem exists with the compression molded tiles of this type. As the cell runs, electrolyte is consumed by corrosive reactions, vaporization, and surface migration. In a typical tile cell, the electrolyte is withdrawn from the larger pores of the matrix. The lithium aluminate cannot be sufficiently close-packed in a tile to achieve a small, uniform pore size at operating temperature by compression molding. Therefore, electrolyte withdrawn from the tile results in contraction of the two-phase structure (matrix and electrolyte), subsequently resulting in the formation of gas pockets which contribute to gas crossover and high internal resistance.
Accordingly, what is needed in this art is a matrix material which is not critically fragile, can withstand flexural and compressive forces during molten carbonate fuel cell assembly, and use, and can achieve a satisfactory inert particle distribution.